This invention relates to cutting tools which are commonly known as files and rasps; rasps are defined as files with individual protruding teeth, whereas files generally have teeth formed by cross-cuts which extend across a face of the file body, usually at an angle, at some regular spacing. The invention is particularly concerned with file/rasps used by ferriers in the treatment and shoeing of hoofed animals, usually horses. Such tools are constructed by upsetting the surface of a steel blank of appropriate size and shape to form rows of tooth-like projections protruding from the rasp side surface of the blank. On the file side of the tool the teeth are formed by upsetting spaced rows of material by making elongated straight cuts (called the over cut) into the blank at regular spacing, usually at a selected angle to the longitudinal center-line of the tool, and then making other cuts (called the upper cuts) across the first set, at a predetermined angle thereto. This results in formation of teeth at the intersections of the cuts. The tool may then be hardened and subsequently the edges of the teeth sharpened by a sand blasting operation.
The resulting teeth have a more or less pointed tip, and in use these tooth tips dull and become rounded, at which point it is virtually imposssible to re-sharpen them and the tool must be discarded. In the prior art, U.S. Pat. No. 94,503 to Nicholson, U.S. Pat. No. 383,999 to Stokes, U.S. Pat. No. 416,805 to Ridge, and U.S. Pat. No. 499,619 to Weed are typical of such pointed rasp teeth. Such teeth are characterized as having either positive or negative angle teeth. This angle is referenced to the slope of the face of the tooth facing the normal direction of cutting; thus a negative or scraping tooth has a face extending upward and rearward to the tooth tip in the direction of cutting, while a positive tooth has a face which is undercut, or extends beneath the tip, so as to slope upward and forward toward the direction of cutting. A negative tooth gives a scraping action with little material removal, a smoothing type of action, while a positive tooth gives a cutting action which will remove material but also may tend to clog with particles of the material forced under the positive tooth. It is important to achieve the best cutting action while also minimizing clogging, and maintaining a sharp tooth tip for as long a use time as possible.
In a tool having a rasp configuration on one side, particularly for ferriers, it is often customary to form a double-cut file surface on the opposite side of the tool blank. British Pat. No. 254,247 (1926) to Ufer and British Pat. No. 456,868 (1936) to Nicholson are typical of such file surfaces.